The present invention relates to a hydraulically driven viscous material pump. More particularly, the present invention relates to a hydraulic system which allows a concrete pump to pump in both a long stroke and short stroke mode.
Concrete pumps are used in a variety of applications in the construction field. Particularly, concrete pumps are used when the concrete must be placed in an area that is physically difficult to approach with a ready mix truck. Due to the nature of concrete, the pump must be rugged and wear resistant, and the flow of concrete must be as continuous as possible. Often, concrete pumps attempt to move the concrete at least every ten minutes and with clearing of the lines being required for stops over thirty minutes to an hour depending on the temperature and the concrete admixture.
Certain types of concrete, such as shotcrete and gunite, are shot at a high velocity under pressure, most often by using air, onto a form or other surface. Shotcreting has been used where a relatively thin section of concrete is needed, such as in shell roofs, walls, tanks, chimneys, swimming pools, jacuzzis, and cover and repair applications for all types of structures. Shotcrete is applied in layers of an inch to an inch and half thick, with the total thickness of up to four inches being obtained by successive placements. With advances in equipment, admixtures and mix designs, many jobs that have traditionally been form and pour are now being shotcreted.
Normally applying standard types of concrete and applying shotcrete require two entirely different types of concrete pumps to apply the material. As a result, contractors are forced to have two kinds of pumps if they wish to apply shotcrete and also work with standard concrete. Requiring two pumps greatly increases the cost to the construction company.